Process for potting electrical circuits

ABSTRACT

A process for potting electrical circuits with asphalt based potting compounds by providing uniform strips of solid potting compound of controlled shape and melt characteristics, which are placed in a container in a certain sequence with the circuit board. The strips, or the uppermost strip is then reflow melted by the application of Infrared Radiant heat from directly above. The melted strip flows into the can, filing all void spaces, potting the circuit.

BACKGROUND OF THE INVENTION

This application pertains to the field of potting compounds forelectrical power apparatuses, especially to the field of pottingcompounds for electrical ballasts for fluorescent lights.

Various compounds are known for potting electrical circuits: that is,encasing an electrical circuit in a container within an imperviousmaterial to protect the circuit from the environment,and/or to improvethe heat dissipation or electrical characteristics of the circuit, or,for electrical power circuits, for electrical safety.

Two major classes of compounds are commonly used. The first are theplastics, especially urethane or epoxy resins. These compounds, whileeffective, have low heat transfer characteristics, and are relativelyexpensive. The second, used in the electrical power and consumerappliance field, is a very inexpensive material, chosen for its low costand good heat transfer and electrical properties. This potting compoundcomprises a mixture of asphalt, silica and, optionally, wax. The primaryinsulating and heat conducting compound is the silica, usually in theform of fine lean sand. Asphalt is used to provide an adhesive for thesand, and, as it melts at a relatively low temperature, to provide aliquid stage for pouring, and, upon cooling, a solid state for thepotting compound. Wax modifies both the melt range of the compound andthe adhesive characteristics of the asphalt, and is therefore present asa modifier for these characteristics.

Asphalt based potting compounds are applied by pouring the liquid,melted compound into a container containing the electrical circuit. Themolten potting compound is usually contained in large, manually operatedpouring pots, which hold the potting compound at the desired melttemperature for best pour characteristics. Such pots must usually bekept heated continuously, because the large thermal inertial of thepotting compound requires too much heat to economically permit cool downand remelting for each day's work. As a result the heated pots requirecontinuous power and monitoring for fire safety in a productionenvironment.

Asphalt based potting compounds are designed to have a high heatconductance, for proper cooling of the encased electrical circuit. Thepotting compound usually has a relatively high specific heat. Electricalcircuits, especially those containing heat sensitive components such assemiconductors or capacitors, have definite upper temperature limits. Asan example, modern electrical fluorescent ballasts have components withan upper temperature range of 290 degrees F. There is therefore at alltimes a narrow temperature range at which the potting compound must beheld to keep it liquid, and yet not overheat the electrical circuit whenthe compound is applied.

The current heat pot method of potting compound application thereforehas several significant disadvantages. The pots must be keptcontinuously at full melt temperature, posing a continual explosion orfire hazard. The pots are expensive, it is estimated that a singleproduction line requires 120,000 dollars solely for the heat pots.Finally, and of equal importance, the process requires manual judgementas to the amount of potting compound poured into each container whichproduces relatively uneven results and quality.

SUMMARY OF THE INVENTION

The invention is a process for applying an asphalt based pottingcompound to an electrical circuit which eliminates the present manualpots, permits a far more precise control of the amount and thetemperature of potting compound applied to the electrical circuit, andreduces the risk of over-temperature damage to the potted electricalcircuit.

Typically, a potted electronic ballast is a single rectangular printedcircuit board, placed in a metal rectangular can (4), closed except atthe top. The potting compound must encase the circuit board, and itscomponents, within the can (4), filling all air spaces within the can(4). The potted circuit should therefore present a uniformly filledappearance, of a can (4) filled with a black smooth material.

The inventive process pots the circuits by providing uniform strips ofsolid potting compound, of controlled shape and melt characteristics,which are placed in the can (4) in a certain sequence with the circuitboard, and which are then reflow melted by the application of InfraredRadiant heat from directly above.

Two distinct strips are provided. An underpour strip is inserted in thecan (4), shaped to fill the bottom of the can (4) below the circuitboard to the edges of the can (4). The circuit board is placed on theunderpour strip. An overpour strip is than placed above the circuitboard. The overpour strip is as long as the circuit board, but isnarrower than the can (4). The filled can (4) is placed on a continuousbelt and passes under a bank of direct radiant heat sources, preferablyInfraRed (IR) heat lamps of controlled radiant power.

The strips comprise selected asphalt-silica-wax compounds. Since thestrips are precut and precast to specific shapes, to match a specificelectrical circuit and can (4) for potting, both the mass of thecompound in each strip, and the strip's thermal characteristics may beexactly controlled. The temperature at which a strip melts may becontrolled by the asphalt used. Further, asphalt melt points may bemodified by oxidizing the asphalt, a known process, and by varying theproportions of asphalt, sand, and wax content. The rate at which thestrip melts under the IR light is then a function of the specific heatof the strip, the melting point of the strip, the power of the IRsource, and time of exposure.

Since the only heat source is from vertically above the covered orshielded (whether directly by the strip or by the tray or bracketholding the strip) electrical circuit can (4), all heat is applied tothe top surface of the overpour strip, which thus melts from its topsurface down. The conveyor speed is set for a desired production rate.The heat output of the IR lamps is easily controlled by varying thevoltage applied to the IR lamps. This voltage control fine tunes theprocess rate so that the overpour strip melts completely just as the can(4) passes voltage from under the last IR heat source.

During the entire process, the overpour strip and a perforated tray orstrip carrier holding the strip receives all the direct radiant heating.The strip carrier shadows and protects the electrical circuit fromover-temperature. The melt point for the overpour strip is chosen to bebelow the maximum permissible temperature of the circuit components, andthus the overpour strip both pots the circuit board and protects thecircuit board from over-temperature during the potting process.

The underpour strip is usually designed to have better adhesion. Heatconduction through the circuit board, from the melted overpour pottingcompound will soften or melt the underpour strip. The circuit board willsettle into the underpour strip, which will then extrude sufficientlyaround the edges of the circuit board to pot the board on its undersideand edges.

An additional advantage to the process is that the overpour strip can bemade of various layers from its upper surface to the bottom. Since thestrip melts from the top down, this permits the final potting compoundto have varying characteristics at various levels within the circuitboard can (4). For example, the upper surface of the overpour strip maybe made having a higher percentage of wax; the resulting pottingcompound will have higher wax content at the surface of the circuitboard, where the additional wax reduces adhesion of potting compound tocomponent wiring next to the circuit board where the wiring is soldered.This reduced adhesion reduces thermally induced mechanical stresses onthe soldered joints as the potted circuit warms up or cools down duringuse, and thus reduces electrical circuit failures.

The increased wax level, however, lowers the thermal conductance of thepotting compound below desirable levels. The next lower layer within theoverpour strip is then of reduced wax content, so that the pottingcompound has a higher thermal conductance. Top down melting of theselayers sequentially reflows the desired potting compound compositiononto the circuit board, permitting the circuit to be potted in a can,with varying potting compound characteristics, as desired, verticallythroughout the potted circuit. Thus a higher heat conductance is formedaround the electrical component bodies, especially the heat producingsurfaces which are generally spaced a distance above the circuit board.

The process is providing distinct underpour potting compound strips andoverpour potting compound strips, placing the circuit board between thestrips in a can and reflow melting the strips controllably into thecircuit containing can by direct radiant heat. The process may beexactly controlled by varying heat exposure by varying the voltageapplied to the radiant heat sources during the heating cycle further,the strips may be made with layers of different characteristics, whichwill melt and deposit as layers of differing characteristics within theelectrical potting. This capability has not previously existed in theart.

It is therefore an object of the invention to disclose a process forpotting electrical circuits which provides a uniform application ofpotting compound to each circuit potted.

It is a further object of the invention to disclose a process forpotting electrical circuits which protects the circuit against theexcessive application of heat.

It is a further purpose of the invention to disclose a process forpotting electrical circuits which has a significantly reduced powerconsumption over the prior art.

It is a further object of the invention to disclose a process forpotting an electrical circuit which produces a potting having reducedsusceptibility to stress cracking of electrical joints at the circuitboard, but which retains maximal thermal conductance and insulatinganti-vibration properties around the high heat generating components inthe circuit.

It is a further object of the invention to disclose a process forpotting an electrical circuit which is capable of producing layershaving desired differing thermal or mechanical properties across thecircuit being potted.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a section view of the circuit board in a can assembled withthe potting compound strips for use in the inventive process. Theunderpour strip is not to scale, for clarity of view of the othercomponents;

FIG. 2 is a view of the two part overpour strip in the process of reflowmelting to pot the circuit board, the underpour strip having melted;

FIG. 3 is a view down the line of the moving belt of the process showingthe use of air blown through the side rails to cool the ends of thecans;

FIG. 4 is a side view of multiple cans being passed by the belt underthe IR lamps in the process;

FIG. 5 is an end view of the underpour strip;

FIG. 6 is an angled view of the underpour strip;

FIG. 7 is an end view of one embodiment of the overpour strip;

FIG. 8 is an angled view of one embodiment of the overpour strip;

FIG. 9 is an end view of a second embodiment of the overpour strip;

FIG. 9A is an angled view of a second embodiment of the overpour strip;

FIG. 10 is an angled view of the can into which the circuit is potted inthe illustrative embodiment of the inventive process;

FIG. 11 is a view of an example circuit board;

FIG. 12 is a bottom view of the example circuit board;

FIG. 13 is a cross section view illustrating the remelt of the overpourstrip; and

FIG. 14 is a view of an assembled circuit board in a can with a two partoverpour strip for remelt in the process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention is best understood in relation to the exactelectrical circuit (2) to be potted and the container (4) into whichthis circuit is to be potted. For the preferred embodiment, the processdescribed is for potting electronic ballasts (2) for fluorescent lamps,and this specific container (4) and circuit board (2) will be describedto illustrate the process.

The exemplar ballast (2) is a rectangular printed circuit board, platedon one side (6), (the bottom) and with all components (8) mounted on theother side (10) (the top). Each component (8) is mounted by passing itsmetal leads (12) through holes in the circuit board (2) and solderingthese leads to the metal interconnections (14) on the circuit board (2).The resulting circuit board (2) therefore has, mounted above its top(10), various components (8) such as transformers, semi-conductors,capacitors; and the like.

This circuit board (2) is placed in a rectangular can or box (4), formedof folded sheet metal. Typically, the can has slightly curved bottomcorners (16), formed by truncating or angling. The ends (18) of the can(4) are merely folded up, and the edge (20) between the ends (18) andthe sides (22) of the can (4) are not necessarily sealed. The can (4) isusually painted black.

Potting of the circuit (2) in the can (4) requires that all surfaces (6,10) of the circuit board (2) are coated with potting compound (24) asthe circuit board (2) is seated in the can. The potting compound (24) isalso used to secure the circuit board (2) in the can (4). The curved orangled bottom can (4) corners (16) serve to space the circuit boardabove the bottom (26) of the can (4) to prevent electrical shorts orflash over between the metal interconnection (14) and the can (4). It istherefore necessary that the potting compound (24) fill the can (4)below the circuit board (2), adhering to both can (4) and board (2). Thecompound (24) then should flow between the edges (28) of the circuitboard and the can (4) side and end walls, and fill the can (4), encasingthe circuit board (2), and leaving no voids.

The potting compound (24) is a mixture of asphalt and silica, withcertain optional additives such as wax to modify the mechanical orthermal properties of the potting compound. The melting point of thecompound (24) is determined primarily by the melting point of theAsphalt, although wax can somewhat affect the melting temperature of thecompound (24). The thermal conductivity of the thermal compound (24) isprimarily determined by the percentage of silica, usually in the form ofclean sand, present in the compound. Increased sand increases thethermal conductivity of the mixture, and therefore increases thepermissible power dissipation of the circuit board (2). Since thecircuit board (2) is encased in the potting compound (24), the maximumelectrical power limits of the circuit (2) will depend on the thermalconductivity of the potting compound (24).

A preferred compound has 60-65 percent silica for proper heat transfer,and 35-40 percent asphalt. The asphalt is selected for a 280 degree Fflow point, or may be modified to such a flow point by selectiveoxidation of the asphalt or varying the ratios of composition. A secondmixture is 50-55 percent silica, 40-45 percent asphalt, and 2-10 percentwax. The asphalt in this mixture has a lessened adhesion, and themixture softens to a plastic state at about 200 degrees F. As abovestated, wax may be added to the above mixtures for better flow rates ofthe melted potting mixture, typically this is a high melting pointsynthetic wax, having a 280 degree F. melt point.

In the inventive process an underpour strip (30) is formed to fit withinthe bottom (26) of the can (4) beneath the circuit board (2). Preferablythe underpour strip (30) is slightly concave (32) along its lengthwiseaxis (34) and has lengthwise border ridges (36) along its sides (38) toprovide extra compound along the edges (28) of the circuit board (2).The underpour strip (30) is formed to contain a fixed quantity ofpotting compound, based on the volume of the can (4) underneath thecircuit board (2) when potted. The volume of the underpour strip (30) iseasily controlled by varying the depth of the lengthwise concavity (32).The underpour strip (30) is preferably made of the 230-260 degree F.softening point compound (24), although it can be formed of the 280degree F. flow point compound (24) if greater heat conductance isrequired under the circuit board (2).

The overpour strip (40) is usually formed of a single thick strip, whichis as long (42) as the circuit board (2), but which is slightly narrower(44) than the board (2). The overpour strip (40) is sufficiently wide(44) however, to cover the components (8) on the board (2), shadowingthem from direct radiant heat (50) from above. The thickness (46) of theoverpour strip (40) is chosen so that the strip (40) contains sufficientpotting compound (24) to fill the can above the circuit board (2),encasing the circuit board (2) and the components (8).

For ease in positioning the overpour strip (40), a covered strip carrier(70) is provided. Strip Carrier (70) has side lips (72) which fit overthe sides (22) of the can (4). The center (74) of carrier (70) isdepressed or concave. Lowered openings (76) permit free flow of remeltedpotting compound (24) into the can (4) while further shielding thecircuit components (8) from radiant heat (50).

A preferred overpour strip (40) is formed as a unitary strip, but havinga higher wax content in a top layer (48) of the strip. Such a strip maybe formed by sequential casting of two mixtures, but is more easilyformed by casting a single strip (40), then casting a layer of wax ontop of the strip (40), and then mechanically mixing the wax layer intothe top of the potting compound (24) as the strip cools.

In the process, a sequence of cans (4) are filled and potted as follows.The cans (4) are aligned transversely (side to side) along a moving belt(52), the cans (4) are retained in alignment on the belt (52) betweentwo side retainer rails (54). In sequence, an underpour strip (30) isplaced in the can (4), a circuit board (2) is placed on the underpourstrip (30), component (8) side up, a strip carrier (70) is placed overthe can (4), and then an overpour strip (40) is placed on the stripcarrier (70) over the components (8). The depressed center (74) of thestrip carrier (70) centers the overpour strip (40) over the can (4) sothat even remelt flow occurs on both sides of the strip (40). The cans(4) then travel on the belt (52), under a direct radiant heat (50)source. A suitable such source (50) comprises a bank of three Infrared(IR) heat lamps (56) such as Sylva-Therm heat lamps by GTE. These lamps(56) have individually an up to one kilowatt radiant power, and may beassembled into infrared ovens (58) by mounting a battery of such lamps(56) within a holder, to be suspended over the moving cans (4) justabove the height of the ballast (4) and overpour strip (40). A bank ofthree sequential such IR ovens (58), totaling 16 kilowatts power, hasproven satisfactory. Individual infrared pyrometers (60) may beperiodically placed between banks of IR lamps (56) to monitor the movingballasts to detect dangerous over-temperature.

The direct IR radiant heat (50) is significantly above the maximumpermissible temperature of the components (8) on the circuit board (2).However, as the belt (52) moves the assembled ballasts (4) below thelamps (56), the strip carrier (70) covers and shadows the componentsfrom direct IR exposure. The angled opening of the Louvered openings(76) permit free flow of melted potting compound (24), but shade againstdirect IR radiation (50). The Overpour strip (40) melts under the directIR heat (50). Starting with the top surface (47) of the overpour strip(40), the melted potting compound (24) flows down the sides (43) of thestrip (42) through the ballast cans (4), filling the space above thecircuit board (2). The temperature of the melted potting compound (24)is the melt point of the overpour strip (40), which is thereforecontrolled to be below the maximum temperature of the components (8) onthe circuit board (2); in the example given, this is 280 degree F. flowpoint, for components (8) having a 290 degree F. maximum temperature.

The speed with which the overpour strip (40) melts is a function of fourfactors: the thermal reflectance of the strip (40); the specific heat ofthe strip (40); the radiant heat power of the IR lamps (56), and thetime of exposure of the strip (40) to the lamps (56). All the pottingcompounds (24) discussed here are a dull black and have a uniformreflectance; any talc coating, which may be present in shipment toprotect individual strips in shipment, melts off at the start and has nosignificant effect on the melting rate of the strips (40). The mass ofthe strip (40) to be melted is determined by the amount of compoundneeded to fill the ballast can (4) and the potting compounds' (24)percentage of silica, chosen for a desired heat conductivity for thepotted ballast. The speed of the belts (52), and thus the time of heatexposure, is fixed to achieve a desired production rate. The radiantheat of the IR lamps is fixed by their design. Therefore it isconsidered best to control the temperature of exposure to achieve adesired melt rate, by varying the voltage applied to the IR lamps (56)and thus vary the radiant heat (50) emitted by the IR lamp (56) so thatthe overpour strip (40) has completely melted just as the ballast can(4) emerges from the last IR lamp.

The underpour strip (30) is preferably of a low softening point pottingcompound (24) as discussed above. Where the underpour strip (30) has a230-260 degree F. softening point, conducted heat from the meltedoverpour strip potting compound (24), through the circuit board (2), issufficient to melt or soften the underpour strip (30), and the circuitboard (2) sinks into the underpour strip (30), sealing and potting thecircuit board (2) from underneath. The underpour strip border ridge (31)extrudes up around the edges (28) of the circuit board, encasing theboard (2) from contact with the can (4) walls.

Where a higher heat conductance is required from the underpour strip(30) than is available from a low melt point potting compound (24), theprocess is modified by first placing the underpour strip (30) in the can(4) and then passing the can (4) and strip (30) under a single IR heatlamp oven (56); where the radiant heat (50) softens the strip (30). Thecircuit board (2) and overpour strip (40) are then placed as before andthe circuit board (2) sinks into the softened underpour strip (30). Theremainder of the process is the same.

A significant advantage of the inventive process over the prior art isthat, since the overpour strip (40) melts from the top down, it can beformed of layers of varying consistency to provide a multi-layer pottingcompound (24) around the circuit (2). For example, in the prior art,circuit failures caused by thermal expansion stress on the componentleads (12) is a recurring problem. An asphalt based potting compound(24) having sufficient thermal conductivity for the circuit components(8) has a high tack or adhesion. It adheres tightly to the componentleads (12) at the point where they are soldered to the circuit board(2), and can stress the leads (12) to cause solder fractures. An asphaltcompound (24) having lessened adhesion, due to the addition of wax, hasinsufficient thermal conductance to dissipate heat from the components(8). The multiple layer strip (40) made possible by the inventiveprocess permits a high wax content potting compound (24) to be meltedand flow onto the circuit board (2) around the lower component leads(12), thus reducing adhesion and thermal stress transfer to the leads(12); a second layer (42) of high silica, high heat conductance compound(24) then melts and pools around the components (8), potting them in adesirable thermal environment.

It is typical for electrical ballasts that the can (4) is formed fromfolded sheet metal. The ends (18) of the can (4) are therefore folded upbut the seams (20) between the ends (18) and the sides (22) are notsealed. This can result in liquid ballast compound (24) leaking betweenthe can (4) ends (18) at these seams (20). This tendency is exacerbatedin the inventive process because ballast cans (4) are painted black toenhance heat dissipation, and thus the cans (4) adsorb heat from the IRlamps (56). It is beneficial therefore to provide a supply of coolingair along or through the side guide rails (54), against which the canends (18) slide as the ballasts (4) are moved through the IR heat ovens(58) on the belt (52). In a simple form, the side rails (54) may beformed of pipes, with small air holes (55) periodically placed, such asat two inch intervals. Cooling air (59) blows from these holes (55) ontothe ends (18) of the ballast cans (4), keeping these ends (18) below themelt temperature of the potting compound (24), and effectively sealingthe end seams against leakage of potting compound (24).

The critical improvement in the process is that the energy consumptionof the potting process is significantly improved by the elimination ofpreheated potting compound pots, with the consequent elimination of thesafety and fire hazards posed by the continual presence of largequantities of molten asphalt based compounds in the factory line.Further, the use of precast strips of potting compound permits exact,repeatable control of the volume and characteristics of the pottingcompound, and exact, repeatable application of a specific quantity ofpotting compound to each circuit and can (4).

The process has been illustrated by the example of use for potting afluorescent ballast into a can. It should be apparent that the processextends to all forms of construction where electrical circuits arepotted using asphalt based potting compounds, which are widely used inthe electrical power industry. The invention thus extends to the widerange of equivalent applications as would be apparent to a skilledworker in the electrical assembly industry.

I claim:
 1. A process for potting an electrical circuit within acontainer comprising the following steps:a) providing an underpour stripof precast, meltable potting compound; b) providing an overpour strip ofprecast, meltable potting compound; c) placing said underpour strip intosaid container; d) placing said electrical circuit onto said under pourstrip within said container; e) placing said overpour strip onto saidelectrical circuit in said container; and f) applying direct radiantheat to the top of said overpour strip until said strip is melted uponsaid electrical circuit.
 2. The process of claim 1 the step of placingthe overpour strip further comprising:placing said overpour strip on alouvered strip carrier; placing said strip carrier on the container,thereby centering the overpour strip above and over the container. 3.The process of claim 1, the step of providing the overpour strip furthercomprising:forming said overpour strip of a plurality o sequentiallayers of potting compound, each layer having differing physicalcharacteristics; said overpour strip melting from the direct radiantheat from the top down, thereby flowing potting compound in layers ontothe circuit, and thus forming potting layers corresponding to the layersin the overpour strip.
 4. The process of claim 3, said overpour striplayers having a top layer having reduced adhesion, and a bottom layerhaving increased thermal conductance, the process comprising:pottingsaid circuit with said potting compound having reduced adhesion aroundcomponent leads, thereby reducing stress cracking of solder joints; andhaving increased thermal conductance around component bodies, therebyincreasing heat dissipation of the potted circuit.
 5. The process ofclaim 3, said overpour strip being provided with a top layer havingincreased wax content and a bottom layer having increased silicacontent, the process further comprising:potting said circuit with saidpotting compound having reduced adhesion, due to wax content, aroundcomponent leads, thereby reducing stress cracking of solder joints; andhaving increased thermal conductance, due to increased silica content,around component bodies, thereby increasing heat dissipation of thepotted circuit.
 6. The process of claim 2, the step of providing theoverpour strip further comprising:forming said overpour strip ofplurality of sequential layers of potting compound, each layer havingdiffering physical characteristics; said overpour strip melting from thedirect radiant heat from the top down, thereby flowing potting compoundin layers onto the circuit, and thus forming potting layerscorresponding to the layers in the overpour strip.
 7. The process ofclaim 6, said overpour strip layers having a top layer having reducedadhesion, and a bottom layer having increased thermal conductance, theprocess comprising:potting said circuit with said potting compoundhaving reduced adhesion around component leads, thereby reducing stresscracking of solder joints; and having increased thermal conductancearound component bodies, thereby increasing heat dissipation of thepotted circuit.
 8. The process of claim 6, said overpour strip beingprovided with a top layer having increased wax content and a bottomlayer having increased silica content, the process furthercomprising:potting said circuit with said potting compound havingreduced adhesion, due to wax content, around component leads, therebyreducing stress cracking of solder joints; and having increased thermalconductance, due to increased silica content, around component bodies,thereby increasing heat dissipation of the potted circuit.
 9. Theprocess of claim 1 further comprising:controlling the rate of melting ofsaid overpour strip by varying the amount of said direct radiant heat.10. A process for potting an electrical circuit within a containercomprising:providing an overpour strip of precast, meltable pottingcompound; placing, in sequence, within the container,said underpourstrip; the electrical circuit; placing said overpour strip on a louveredstrip carrier; placing said strip carrier on the container, centeringthereby said strip over the container; forming thereby a can assembly;placing a sequence of said can assemblies on a moving belt; moving, onsaid belt, said can assemblies past and under one or more radiant IRheat ovens, thereby:melting said overpour strip from the top down;filling the container from the top of the circuit board with meltedpotting compound; shielding said circuit board from direct radiant heatby shadowing from said louvered strip carrier; conductively heating,from the heat of the melted overpour strip, said underpour strip untilsaid underpour strip softens, thereby setting said circuit board intosaid underpour strip, thereby potting said circuit board in saidcontainer.
 11. The process of claim 10, the step of providing theoverpour strip further comprising:forming said overpour strip of aplurality of sequential layers of potting compound, each layer havingdiffering physical characteristics; said overpour strip melting from thedirect radiant heat from the top down, thereby flowing potting compoundin layers onto the circuit, and thus forming potting layerscorresponding to the layers in the overpour strip.
 12. The process ofclaim 11, said overpour strip layers having a top layer having reducedadhesion, and a bottom layer having increased thermal conductance, theprocess comprising:potting said circuit with said potting compoundhaving reduced adhesion around component leads, thereby reducing stresscracking of solder joints; and having increased thermal conductancearound component bodies, thereby increasing heat dissipation of thepotted circuit.
 13. The process of claim 10, said overpour strip beingprovided with a top layer having increased wax content and a bottomlayer having increased silica content, the process furthercomprising:potting said circuit with said potting compound havingreduced adhesion, due to wax content, around component leads, therebyreducing stress cracking of solder joints; and having increased thermalconductance, due to increased silica content, around component bodies,thereby increasing heat dissipation of the potted circuit.
 14. A processfor potting an electrical circuit within a container comprising thefollowing steps:a) providing an underpour strip of precast, meltablepotting compound; b) providing an overpour strip of precast, meltablepotting compound; c) placing said underpour strip into said container;d) applying direct radiant heat to said underpour strip until said stripis melted; e) placing an electrical circuit onto said melted underpourstrip within said container; f) placing said overpour strip onto saidelectrical circuit in said container; and g) applying direct radiantheat to the top of said overpour strip until said strip is melted uponsaid electrical circuit.
 15. A process for potting an electrical circuitwithin a container comprising:providing an underpour strip of precast,meltable potting compound; providing an overpour strip of precast,meltable potting compound; in sequence, first placing within thecontainer said underpour strip; placing a sequence of said containerswith said underpour strips on a moving belt; moving, on said belt, saidcontainers past and under one or more radiant IR heat ovens,thereby:melting said underpour strip; next placing within the container,on top of said melted underpour strip, an electrical circuit; thenplacing said overpour strip on a louvered strip carrier, and placingsaid strip carrier on the container, centering thereby said strip overthe container; forming thereby a can assembly; placing a sequence ofsaid can assemblies on a moving belt; moving, on said belt, said canassemblies past and under one or more radiant IR heat ovens,thereby:melting said overpour strip from the top down, filling thecontainer from the top of the circuit board with melted pottingcompound, thereby potting said circuit board in said container whileshielding the circuit board from direct radiant heat by shadowing fromsaid louvered strip carrier.